OBJECTIVE: The study compared the burden that specific problem behaviors of patients with schizophrenia or bipolar disorder placed on relatives and evaluated the accuracy of mental health professionals' judgment of the burden. METHODS: A questionnaire was developed to assess the burden of 20 common problem behaviors associated with manic, positive, and negative symptoms. The questionnaire was given to 48 relatives of patients with schizophrenia or bipolar disorder. In addition, 39 mental health professionals completed separate questionnaires indicating the amount of burden they believed relatives experienced due to these behaviors. RESULTS: Relatives of patients with bipolar disorder rated manic symptoms as more burdensome than did relatives of patients with schizophrenia, but relatives of patients in the two groups did not differ in their ratings of burden associated with positive or negative symptoms. Professionals' perceptions of the burden associated with manic symptoms were relatively accurate, but they tended to underestimate the burden of positive and negative symptoms experienced by relative of patients with bipolar disorder. CONCLUSIONS: Psychiatric diagnosis may be of limited value in understanding the burden relatives experience due to specific psychiatric symptoms. Professionals are encouraged to assess the burden that is associated with specific problem behaviors regardless of psychiatric diagnosis.